Optical microscope stage for scanning probe microscope

ABSTRACT

Scanning probe microscopes and scanning probe heads are provided having improved optical visualization and sample manipulation capabilities. The SPMs and SPM heads include at least one flexure stage for scanning in the x, y and/or z directions. In a preferred embodiment, the SPMs or SPM heads include flexure stages for scanning in the x, y and z directions. The z scanning stage is preferably positioned outside the lateral footprint of the x-y flexure stage so that a probe extending from the z scanning stage is outside the lateral footprint of the instrument. The SPMs and SPM heads are configured to provide top down and bottom up optical views of the sample and/or the probe and enable simultaneous scanning probe microscopy and optical imaging of a sample to be performed. The SPMs and SPM heads are designed to be readily combinable with existing upright and inverted optical microscopes currently available from various major manufacturers.

This application is a continuation of Ser. No. 08/808,351 filed Feb. 28,1997 now U.S. Pat. No. 5,854,487.

FIELD OF THE INVENTION

The present invention relates to a scanning probe microscope (SPM) whichemploys one or more flexure stages and providing enhanced optical viewsof the probe and sample.

BACKGROUND OF THE INVENTION

Scanning probe microscopes (SPMs) are designed to sense one or morephysical properties of a surface at a high degree of resolution in orderto provide a detailed analysis of the topographical or other propertiesof a surface. Using scanning probe microscopy, it is possible to detectphysical features on the scale of individual atoms and molecules. Amongthe physical properties which SPMs can image are attractive andrepulsive forces due to interatomic forces, electrical potentials,magnetic forces, capacitive forces, and conductive, optical and thermalproperties. In addition to detecting physical properties of a surface,SPMs can be used in a variety of applications including the imaging andprocessing of semiconductors, magnetic materials and storage media,biological materials, polymers, coatings, metals and the like. SPMs arealso used in surface science, materials science, crystal growth,electrochemistry and other studies of surfaces. SPM imaging may beperform in ambient, liquid and vacuum environments.

In general, SPMs include a probe which is positioned in very closeproximity to a sample surface in order to detect one or more of theabove topographic or physical properties of the surface. For example, inscanning force microscopes (SFM), also commonly referred to as atomicforce microscopes (AFM), the probe includes a tip which projects fromthe end of a cantilever and is used to detect interatomic forces betweenthe probe tip and the sample. Typically, the tip is very sharp in orderto achieve maximum lateral resolution by confining the force interactionto the end of the tip. A detection system is used to detect thedeflection of the cantilever in order to determine the contours of thesurface property being probed. In scanning tunneling microscopes (STM),the probe includes a sharp conductive needle-like tip which is used tomeasure tunneling current flowing between the tip and a conducting orsemiconducting sample surface. In STMs, the tip is typically positionedonly a few Angstroms above the surface being probed.

The scanning operation of an SPM is performed by a fine x,y,z stage, orscanner. The scanner typically moves the sample or probe in the x-yplane such that the probe follows a raster-type path over the surface tobe analyzed. In many SPMs, the scanning movement is generated with apiezoelectric tube. The base of the tube is fixed, while the other end,which may be connected to either the probe or the sample, is free tomove both laterally and as vertically input voltage signals are appliedto the piezoelectric tube. The use of a piezoelectric tube in thisapplication is well known and is described, for example, in an articleby Binnig and Smith, Rev. Sci. Instrum., 57 1688 (1986). An SPM may beoperated under feedback control, whereby a feedback controller maintainsa constant separation between the probe and sample during a scan byadjusting the z position of the z scanning stage.

A key issue common to all SPMs is the accurate positioning and movementof the probe relative to the sample surface in the x, y and zdirections. Movement of the probe and sample relative to each other maybe performed by moving the probe, the sample or both the probe andsample. A need exists for SPMs which provide highly accurate scanning inthe x, y and z direction. One significant problem in this regard iscross coupling between different scan directions. A need thereforeexists for a scanning mechanism which enables the probe and sample to bescanned relative to each other with minimal cross coupling.

The ability to optically view a probe and/or sample before during orafter scanning probe microscopy is an important feature of an SPM.Optical viewing facilitates a variety of functions associated withscanning probe microscopy including, for example, coarse adjustment ofseparation between the probe and the sample, coarse adjustment of thesample position laterally relative to the probe, manipulation of thesample without having to remove the sample or disassemble the instrumentand alignment of the cantilever deflection detection system. A needtherefore exists for an SPM which is designed to provide enhancedoptical viewing of the sample and/or probe in an SPM including thecapability to perform optical imaging using the various optical modes ofan optical microscope. These and other objectives are provided by thepresent invention.

SUMMARY OF THE INVENTION

The present invention relates to scanning probe microscopes (SPM) andscanning probe microscope heads (SPM heads) having improved opticalvisualization and sample manipulation capabilities. Scanning probemicroscopy may be performed using the SPMs and SPM heads of the presentinvention by any mode of SPM imaging including, but not limited tocontact atomic force microscopy (AFM), non-contact AFM, lateral forcemicroscopy (LFM), scanning tunneling microscopy (STM), magnetic forcemicroscopy (MFM), scanning capacitance microscopy (SCM), forcemodulation microscopy (FMM), electrostatic force microscopy (EFM), phaseimaging and other modes of operating a scanning probe microscope.

In one embodiment, the SPM or SPM head includes a x-y flexure stage. Thex-y flexure stage may be a single plate biaxial flexure stage and ispreferably a stacked x-y flexure stage. The SPM or SPM head alsoincludes a z scanning stage for scanning a probe in the z directionrelative to a sample.

In one variation of this embodiment, the z scanning stage is positionedoff-center relative the a lateral footprint of the x-y flexure stage andmore preferably outside the lateral footprint of the x-y flexure stage.

In another variation of this embodiment, the probe is positionedoff-center relative to a lateral footprint of the x-y flexure stage,more preferably outside the lateral footprint of the x-y flexure stage,most preferably outside the lateral footprints of the x-y flexure stageand z scanning stage.

In another variation of this embodiment, the z scanning stage is a zflexure stage. In a preferred embodiment of this variation, the zflexure stage is positioned off-center relative to a lateral footprintof the x-y flexure stage and more preferably outside the lateralfootprint of the x-y flexure stage.

In another variation of this embodiment, the SPM or SPM head includesmore than one z scanning stage. In a preferred variation, the multiple zscanning stages are z flexure stages.

In another embodiment, the SPM or SPM head includes an x-y scanningstage and one or more z flexure stages. In one variation of thisembodiment, the one or more z flexure stages are positioned off-centerrelative to a lateral footprint of the x-y scanning stage and morepreferably outside the lateral footprint of the x-y scanning stage.

In any of the above embodiments, the SPM or SPM head may include an x-yscanning stage, a z scanning stage attached to the x-y scanning stagehaving z sides extending laterally from the x-y scanning stage andhaving an end distal to the x-y scanning stage, and a bracket containingan SPM probe coupled to the z scanning stage. In one variation, thebracket is mounted to one of the sides of the z scanning stage. Bymounting the probe on a bracket in this manner, the distance between theprobe and a distant side of the x-y scanning stage is reduced relativeto mounting the probe on the distal end of the z scanning stage. Thebracket may also include a detection system for the probe.

In any of the above embodiments, a closed loop scanning system isincorporated into the SPM or SPM head.

In any of the above embodiments, the SPM head may be designed to be astand-alone sensor head which is supported on three or more legs. Inthis embodiment, the sample is placed on a surface underneath the SPMhead. In another embodiment, the sample stage may be an optical stage ofan upright or inverted optical microscope.

One feature of the SPMs and SPM heads of the present invention is thatthey can be configured to provide unobstructed top down and bottom upoptical views of the sample and/or the probe.

Another feature of the SPMs and SPM heads of the present invention isthat they can be configured to enable simultaneous scanning probemicroscopy and optical imaging of a sample to be performed using avariety of optical modes of an optical microscope.

Another feature of the SPMs and SPM heads of the present invention isthat they are designed to be readily combinable with existing uprightand inverted optical microscopes currently available from various majormanufacturers. In one embodiment, an SPM head of the present inventionis coupled to an optical microscope where in the stage of the opticalmicroscope serves as the sample stage for the SPM head.

Another feature of the SPMs and SPM heads of the present invention isthat they may be used with a variety of modes of an optical microscope.For example, the SPMs and SPM heads may be used to perform probescanning coupled with epi illumination and an upright opticalmicroscope; epi illumination and an inverted optical microscope;transmissive illumination and an upright optical microscope; andtransmissive illumination and an inverted optical microscope.

Another feature of the SPMs and SPM heads of the present invention istheir ability to be configured to provide working distances as short as10 mm and as short as 20 mm when a liquid cell is incorporated into theSPM.

Another feature of the SPMs and SPM heads of the present invention istheir ability to be configured to provide improved physical access to asample so that different tools can be used to manipulate the sampleand/or measure properties of the sample. For example, the SPMs and SPMheads can include modifications, such as indentations to permit accessof tools to the sample during microscopy.

Another feature of the present invention is that an objective lens andan illumination source may be positioned relative to a probe and sampleof an SPM or SPM head to provide either epi or transmitted (Kohler)illumination with simultaneous probe scanning.

Another feature of the present invention is that the SPMs and SPM headsof the present invention can be configured to provide simultaneousprobe-scanned SPM with an unobstructed optical view obtained without theassistance of a reflective surface.

Another feature of the present invention is that simultaneousprobe-scanned SPM and epi illumination using a standard commerciallyavailable upright optical microscope is enabled.

Another feature of the present invention is that simultaneousprobe-scanned SPM and transmitted illumination using standardcommercially upright and inverted optical microscope is enabled.

Another feature of the present invention is that simultaneousprobe-scanned SPM and all the optical modes provided by standardcommercially available upright and inverted optical microscopes isenabled.

The present invention also relates to a dual mirror optical deflectiondetection system. The detection system includes two steerable mirrors,one mirror to steer the laser beam from the laser to the cantilever, andthe second mirror to steer light reflected off the cantilever to thedetector. In one variation, the laser of the detection system isoriented horizontally, i.e., approximately parallel with the x-y plane.This orientation minimizes the laser's dimensions along the z axis.

An unique aspect of the dual mirror optical deflection detection systemis that the area above the cantilever probe is unobstructed. As aresult, the space substantially above the cantilever probe is free forboth illumination and for direct optical inspection.

In another embodiment, an SPM or SPM head of the present inventionincludes a locking jack for raising and lowering the head of the SPMrelative to the sample stage. The locking jack includes an arm attachingthe SPM head to the stage, a spring which biases two or more legs of theSPM head against a surface on which the SPM head is placed, and alocking mechanism which holds the SPM head in a raised position. In thisembodiment, the sample stage preferably includes a kinematic mount whichallows the SPM head to be raised and lowered relative to the samplestage without having to adjust the positioning of the probe relative tothe sample after lowering the SPM head.

The present invention also relates to a sample stage and sample holderdesigned for use in biological applications. The sample holder mayinclude one or more slots sized to accommodate a coverslip or slideand/or one or more depressions sized to accept a Petri dish. Springclips or other securing mechanisms may be used to secure a slide in aslot or a Petri dish in a depression.

The sample stage may also include a ring member which is slidable on thesample stage. The ring member is sized to fit around a sample holdersuch that the sample holder can be positioned within the ring member andmoved in the plane of the sample stage by the ring member. The ring ispreferably larger than the sample holder so that the sample holder canbe disengaged from the ring member for greater mechanical stabilityduring SPM imaging.

The present invention also relates to a combined liquid cell/cantileverchip holder for use in an SPM or SPM head. The liquid cell includeswalks which are preferably sized to fit beneath a condenser lens orobjective of an optical microscope. The bottom of the liquid cellincludes the viewport through which the cantilever probe and samplemaybe viewed.

The liquid cell is designed to provide a clear path for the laser beamof an optical deflection detection system through the viewport to thecantilever probe. The liquid cell may also include indentations madealong the length of the walls to allow easy access to a sample using atool.

The liquid cell cantilever holder is preferably kinematically mounted tothe SPM head. As a result, the cantilever holder can be accurately andrepeatably positioned on the SPM head, and cantilevers can be replacedwith minimal realignment of the cantilever deflection detection system.In addition, the cantilever holder can be removed from the SPM headeasily by hand without the assistance of tools. This feature isadvantageous for use in a variety of applications including thesemiconductor process control equipment and applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of an SPM head according to the presentinvention.

FIG. 2 illustrates a top down view of an embodiment of an SPM headaccording to the present invention in which the probe is mounted on thez flexure stage by a bracket that extends off the end of the z flexurestage.

FIG. 3 illustrates a top down view of an alternate embodiment of the SPMhead illustrated in FIG. 2 in which the probe is mounted on the zflexure stage by a bracket that extends off a side of the z flexurestage.

FIG. 4 illustrates an embodiment of an SPM according to the presentinvention.

FIG. 5 illustrates an embodiment of a flexure stage which providesmotion in a single transnational direction.

FIG. 6 illustrates an embodiment of a single-plate biaxial flexure stagewhich provides motion in a two translational directions.

FIG. 7 illustrates a stacked x-y flexure stage.

FIG. 8 illustrates a tripod scanner.

FIGS. 9A-9B illustrate two sources of z displacement during the scanningmotion of a piezoelectric tube scanner.

FIG. 9A illustrates the effect of bowing in a piezoelectric tubescanner.

FIG. 9B illustrates the push-pull effect in a piezoelectric tubescanner.

FIG. 10 illustrates the positioning of a z scanning stage at the centerof motion of an x-y scanning stage.

FIG. 11 illustrates an embodiment of a z flexure stage.

FIG. 12 illustrates a lateral view of an SPM head where the z flexurestage is positioned outside the lateral footprint of the x-y scanningstage.

FIGS. 13A-B illustrate a dual mirror optical deflection detectionsystem.

FIG. 13A illustrates a top down view of the detection system.

FIG. 13B illustrates a lateral view of the detection system.

FIG. 14A illustrates the effect of mounting the laser verticallydirectly over the probe.

FIG. 14B illustrates the effect of mounting the laser vertically offsetfrom the probe.

FIG. 15 illustrates that the diameter of the laser and the photodetectorare the limiting factors with regard to the height profile of thedetection system

FIG. 16 illustrates the incorporation of a closed loop scanning systeminto the SPMs and SPM heads of the present invention.

FIG. 17 illustrates a kinematically mounted SPM head on a coarse x-ymechanical stage.

FIGS. 18A-B illustrate a mechanism for raising and lowering a SPM headrelative to a stage.

FIG. 18A illustrates the SPM head in a lowered position.

FIG. 18B illustrates the SPM head in a raised position.

FIGS. 19A-19C illustrate embodiments of sample stages and sample stageholder designed for use in biological applications of scanning probemicroscopy.

FIG. 19A illustrates a sample holder which includes slots sized toaccommodate a coverslip or slide as well as a depression which accepts aPetri dish.

FIG. 19B illustrates a sample holder which includes multiple slots sizedto accommodate a series of coverslips or slides.

FIG. 19C illustrates a sample holder which includes multiple depressionssized to accommodate a Petri dish.

FIGS. 20A-B illustrate the sliding movement of a sample over a samplestage using a ring to push and pull the sample.

FIG. 20A illustrates the sliding motion of the sample holder (sideview).

FIG. 20B illustrates the sample being pushed by the ring over the samplestage.

FIGS. 21A-21C illustrate a combined liquid cell/cantilever chip holderfor use in an SPM or SPM head.

FIG. 21A illustrates an embodiment of a liquid cell.

FIG. 21B illustrates another embodiment of the liquid cell whichincludes indentations made along the length of the body to allow easieraccess to the sample using a long narrow tool.

FIG. 21C illustrates a combined liquid cell/cantilever chip holder whichallows decreased lens working distance.

FIG. 22 illustrates a kinematic mount for a liquid cell/cantilever chipholder.

FIG. 23A illustrates a cantilever directly mounted on a cantileverholder.

FIG. 23B illustrates a cantilever kinematically mounted on a cantileverholder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to scanning probe microscopes (SPM) andscanning probe microscope heads (SPM head) having improved opticalvisualization and sample manipulation capabilities.

The SPMs and SPM heads of the present invention are designed to provideboth top down and bottom up unobstructed optical views. In an SPM or SPMhead, top down and bottom up optical views are very useful for aligningthe probe over the sample and for selecting a region on the sample forscanning.

The SPMs and SPM heads of the present invention are also designed toenable simultaneous scanning probe microscopy and optical imaging of asample to be performed. For simultaneous SPM and optical imaging, a topdown optical view is particularly useful for correlating features in theoptical image and the SPM image. U.S. Pat. Nos. 5,376,790 and 5,157,251provide useful discussions regarding the importance of optical viewingin conjunction with performing scanning probe microscopy and areincorporated herein by reference.

The SPMs and SPM heads of the present invention are also designed to bereadily combinable with existing upright and inverted opticalmicroscopes currently available from various major manufacturers. Forexample, an SPM or SPM head may be coupled to an optical microscopewhere the stage of the optical microscope serves as the sample stage forthe SPM. This embodiment is particularly well suited for use inapplications where simultaneous viewing and probing are desired.

The SPMs and SPM heads of the present invention are also designed to beusable with all modes of an optical microscope. For example, the SPMsand SPM heads may be used to perform probe scanning coupled with epiillumination and an upright optical microscope; epi illumination and aninverted optical microscope; transmissive illumination and an uprightoptical microscope; and transmissive illumination and an invertedoptical microscope.

The SPMs and SPM heads of the present invention are designed to achievenanometer-scale resolution. Resolution down to the atomic scale is alsopossible according to the present invention.

Some embodiments of the SPMs and SPM heads of the present invention aredesigned to have a smaller lateral footprint. A smaller lateralfootprint provides the instrument with a smaller mechanical loop, i.e.,the path between the support structure of the sample and that of theprobe on the instrument. By reducing the mechanical loop of theinstrument, mechanical stability due to increasing the lowest naturalresonance of the instrument is increased, and thermal instability due tothermal expansion and contraction of the instrument are reduced.

The SPMs and SPM heads of the present invention are also designed toimprove physical access to a sample so that different tools such asmicromanipulators, patch clamp pipettes and pH probes can be used tomanipulate the sample and/or measure properties of the sample near theprobe of the SPM or simultaneously during imaging. In the case ofbiological samples, the improved access to the sample also facilitatesthe manipulation of cell structures while mounted in the SPM. The SPMsand SPM heads can also include modifications, such as indentations topermit access of micromanipulators, patch clamp pipettes, and othertools used for the micromanipulation of cells.

Scanning probe microscopy may be performed using the SPMs and SPM headsof the present invention by any mode of scan probe imaging including,but not limited to contact atomic force microscopy (AFM), non-contactAFM, lateral force microscopy (LFM), scanning tunneling microscopy(STM), magnetic force microscopy (MFM), scanning capacitance microscopy(SCM), force modulation microscopy (FMM), phase imaging, electrostaticforce microscopy (EFM), and other modes of operating a scanning probemicroscope.

Optical viewing of the probe and sample may be performed by any mode ofoptical viewing microscopy including, but not limited to confocalmicroscopy, phase contrast microscopy, differential interferencecontrast microscopy, Hoffman/modulation contrast microscopy, and otheroptical modes.

In one particular embodiment, the SPM head is designed to be astand-alone sensor head which is supported on three or more legs. Inthis embodiment, the SPM head is set on a sample stage. In one variationof this embodiment, the sample stage is an optical stage of an uprightor inverted optical microscope and the sample to be imaged is supportedon the optical microscope stage. This embodiment is particularly wellsuited for use in a variety of biological applications, including, forexample, patch clamp cell physiology applications. The opticalmicroscope stages are also well-designed for standard sample holdersused in biological imaging, for example, Petri dishes, glass slides,multiwell plates, and the like. However, it should be noted that thisstand alone SPM head embodiment can be used with any SPM imagingapplication.

One aspect of the design of the SPMs and SPM heads which enable top downand bottom up unobstructed optical views of the probe and sample is thelow height profile of the SPMs and SPM heads. The low height profilereduces the working distance at which an optical lens and/or anillumination source must be positioned from the sample or probe. As aresult, standard objective lenses and condenser lenses can be used withthe SPM because the lens can be brought sufficiently close to the probefor the probe to be within the lens's focal length. For example, theSPMs and SPM heads of the present invention provide working distances asshort as 10 mm and as short as 20 mm when a liquid cell is incorporated.

Another important aspect of the present invention is the use of an offcenter geometry for the z scanning stage relative to the x-y scanningstage in the SPMs and SPM heads, i.e., the offset positioning of the zscanning stage relative to the center of translation of the x-y scanningstage. In a preferred embodiment, the z scanning stage is positionedlaterally external to the x-y scanning stage. By positioning the zscanning stage off center and preferably external to the x-y scanningstage, improved access to the probe and sample is enabled. In addition,the angular range of the field of view of the probe and sample isimproved. Further, the working distance at which a lens for opticalviewing and/or an illumination source can be placed relative to theprobe and sample is reduced by having the z scanning stage laterallydisplaced relative to the x-y scanning stage.

Another important aspect of the present invention is the off centergeometry of the probe relative to the x-y scanning stage. In a preferredembodiment, the probe is positioned laterally external to the x-yscanning stage, and more preferably external to the x-y and z scanningstages. By positioning the probe off center and preferably external tothe x-y and/or x-y and z scanning stages, improved access to the probeand sample is enabled. In addition, the angular range of the field ofview of the probe and sample is improved. Further, the working distanceat which a lens for optical viewing and/or an illumination source can beplaced relative to the probe and sample is reduced by having the probelaterally displaced relative to the x-y or x-y and z scanning stages.

Another important aspect of the present invention is the use of an x-yflexure stage in the SPMs and SPM heads to produce a scanning motion ofa probe relative to a stationary sample. One advantage of x-y flexurestages is that it provides highly planar, orthogonal motion by the probeover a surface in the x-y plane. The planarity of the scan produced byx-y flexure stages is particularly improved as compared to tube scannerand tripod scanner designs. X-Y flexure stages also provide minimalcoupling with motion in the z axis. As a result, the probe and a stagewhich provides scanning along the z axis can be laterally displacedrelative to the center of motion of the x-y flexure stage which providesthe optical viewing and sample handling and manipulation advantages asdescribed above.

Another advantage of x-y flexure stages is the low height profileprovided by these stages as compared to tube scanners. As describedabove, a low height profile facilitates the provision of top down andbottom up unobstructed optical views by the SPMs and SPM heads of thepresent invention.

The x-y flexure stages used in the SPMs and SPM heads of this inventionmay be either a stacked x-y flexure stage or a single-plate biaxial x-yflexure stage.

Single-plate biaxial x-y flexure stages have an advantage over stackedx-y flexure stages of having a lower height profile.

Stacked x-y flexure stages have several advantages over single-platebiaxial x-y flexure stages. For example, stacked x-y flexure stages aremore easily designed, have a smaller lateral footprint, are lesssusceptible to thermal drift, provide more orthogonal scanning motion inx and y, exhibit greater decoupling in the x, y, and z scan directions,and are less expensive to manufacture.

Another important aspect of the present invention is the use of one ormore z flexure stages to produce a scanning motion of a probe attachedto the SPM in the z direction relative to a stationary sample.

In the SPMs and SPM heads of the present invention, the one or more zflexure stages are preferably offset relative to the center oftranslation [(x,y)=(0,0)] of the x-y scanning stage. This design featureenables the SPMs and SPM heads to be designed to provide improved accessto the probe and sample. Improved probe and sample access, in turn,facilitates the use of upright and inverted optical microscopes toprovide top down and bottom up optical viewing with, for example, epi ortransmissive illumination. The offset positioning of the z flexure stagealso facilitates the manipulation of the sample and replacement of theprobe.

Laterally offsetting the z stage relative to the center of translationof the x-y scanning stage requires that the scan provided by the x-yscanning stage be substantially perpendicular to the z axis throughoutits scanning field. In this regard, it is preferred to use a x-y flexurestage which provides a highly planar scan in combination with an offsetz flexure stage. In a particularly preferred embodiment, a stacked x-yflexure stage is used as the x-y scanning stage in order to takeadvantage of the above described advantages of using a stacked x-yflexure stage.

In one embodiment of the invention, the SPMs and SPM heads are designedfor use in biological applications. In particular, the SPMs and SPMheads of this embodiment are designed for the study of live cellcultures, protein assemblies, protein-DNA complexes, and nanodissectionof cells, chromosomes, and protein assemblies.

In another embodiment of the invention, the SPMs and SPM heads of thepresent invention include a low profile dual mirror optical deflectiondetection system mounted on a z scanning stage. In this detectionsystem, two steerable mirrors are used to steer a laser beam from alaser onto a cantilever and then onto a detector. Key novel features ofthe optical deflection detection system include a horizontal orientationof the laser in the detection system and the use of dual mirrors in aprobe scanning SPM to steer the laser beam from the laser to thecantilever and then to the detector.

The orientation and spacing of the elements used in the detection systemenables SPMs and SPM heads which employ this detection system to includea space substantially above the probe that may be used to provide anunobstructed optical view of the probe such that direct opticalinspection of the probe with a magnification lens or other opticalinstrumentation is possible. Accordingly, a magnified optical view ofthe probe can be achieved without the use of a reflective element.

The present invention also relates to the use of a coarse x-y controlstage in combination with a SPM or SPM head which is used to align thecantilever over or under an objective lens of an optical microscope. Inone embodiment of the invention, an SPM head is used in combination withan optical microscope wherein the stage of the optical microscope isused as the sample stage for the SPM head. In this embodiment, the SPMhead is preferably coupled to the optical microscope stage by a lockingjack which allows the SPM head to be raised and lowered relative to thesample stage in order to provide rapid probe and sample access forreplacement or manipulation. In this embodiment, the optical microscopestage is also preferably designed to include a kinematic mount thatallows the SPM head to be raised and lowered relative to the samplestage without having to adjust the positioning of the probe relative tothe sample after raising the SPM head.

The present invention also relates to a ring member which can be slid onthe surface of a sample stage and be used to move a sample holderpositioned within the ring member on the sample stage by sliding thering member relative to the surface.

The present invention also relates to a kinematically mounted liquidcell. This liquid cell can be magnetically attached to the SPM,springloaded, or used with some other mechanical attachment. It canallow simultaneous optical and SPM inspection of a sample while in anaqueous solution. It can also incorporate a fluid exchange mechanism. Inthis preferred embodiment it can be easily replaced when coupled withthe above described locking jack mechanism.

The present invention also relates to a kinematically mounted cantileverchip holder which enables easy cantilever chip replacement. Thequick-snap self-seating mechanism is useful for a variety of SPM's andinspection systems, including semiconductor process control equipmentand applications. The kinematically mounted cantilever chip holder canalso be used to facilitate an automatic tip changer which would bemotorized, requiring no human physical contact to replace and align thecantilever holder since the holder can be pulled out easily withoutspecial tools and can be returned to a predefined position on theinstrument without tools or the need for further adjustment.

In any of the embodiments described in this application, standardelectronics used to operate existing SPMs and SPM heads may be used.

FIG. 1 illustrates an embodiment of an SPM head 12 according to thepresent invention which is positioned on a surface 14 containing asample 16. As illustrated in FIG. 1, the SPM head includes an x-yscanning stage 18, a z scanning stage 20, and a probe 22 offset relativeto the x-y scanning stage 18 and z scanning stage 20. As illustrated,the low height profile 24 of the SPM head 12 inclusive of legs 19enables an objective lens 26, 26′ of an optical microscope or anillumination source for a microscope to be positioned within a shortworking distance 28, 28′ above or below the probe 22 and sample 16,thereby enabling the sample to be simultaneously probed and visuallyobserved. As also illustrated, the offset geometry of the probe 22relative to the SPM head enables the sample to be visually observed froma position 30 above the sample 16 and from a position 32 below thesample 16.

FIG. 2 illustrates a top down view of an embodiment of an SPM head 12where the probe 22 extends from a bracket 34 positioned at a side of thez scanning stage 20. As illustrated, positions above 30 and below 32 thesample 16 are not obstructed by the SPM head and thus can be visuallyobserved by positioning an optic 26 above and/or below the probe andsample 16. As also illustrated, the probe 22 is laterally offsetrelative to the z scanning stage 20 which reduces the length 21 of theSPM head along a direction extending from the probe 22 to the distantside of the x-y scanning stage 18.

FIG. 3 illustrates an alternate embodiment of an SPM head in which theprobe 22 is mounted on a bracket 36 which extends off the end of the zscanning stage 20. The distance from the probe to the opposite end ofthe SPM head is given as length 23 in FIG. 3. This configuration isadvantageous in that the probe is mounted on a shorter, more rigidextension from the x-y scanning stage which provides improved mechanicalperformance.

The orientation of the probe relative to the x-y and z scanning stagesis an important design aspect of the present invention. In general, itis desirable to have the probe pointing towards the user in the opticalview in order to facilitate the user to steer and align the laser beamonto the back of the cantilever. The distance from the probe to theopposite end of the SPM head is significantly longer in the designillustrated in FIG. 3 (length 23) than in FIG. 2 (length 21). As aresult, an SPM head having a design as illustrated in FIG. 3 where theprobe extends from an end of the z flexure stage may have difficultyfitting on some optical microscope stages. For instance, the condensercolumn of inverted optical microscopes is usually situated at the backof the microscope stage. This location restricts the space available toplace the SPM head.

The configuration of FIG. 2 where the probe is rotated by 90° relativeto the x-y scanning stage is preferred over the configurationillustrated in FIG. 3 because the distance from the probe to the rearedge of the x-y scanning stage is significantly reduced. As a result,the SPM head design can more readily fit under the lenses of mostoptical microscopes.

FIG. 4 illustrates an embodiment of an SPM 42 according to the presentinvention. As illustrated, the SPM includes sensor head 42 whichincludes an x-y scanning stage 44, a z scanning stage 46, and a probe 48offset relative to the x-y scanning stage 44 and z scanning stage 46. Asillustrated, the sensor head 42 has a low height profile 49 whichenables an objective lens 50, 50′ of an optical microscope to bepositioned within a short working distance 52, 52′ from the probe 48.The SPM also includes a sample stage 54 on which a sample 56 may bepositioned. As also illustrated, the off-set geometry of the probe 48relative to the sensor head 42 enables the sample to be visuallyobserved from a position 30 above the sample 16 and from a position 32below the sample 16.

The SPM head also includes a cantilever deflection detector 45. The SPMhead 42 is supported on legs 43 and may be set on a surface 47 such asan optical microscope stage.

X-Y Flexure Stage

One important aspect of the present invention is the use of x-y flexurestages in the SPMs and SPM heads which provide the probe with a scanningmotion in the x and y directions. By using an x-y flexure stage, SPMsand SPM heads of the present invention have a highly planar, orthogonalscanning motion which is substantially perpendicular to the z axisthroughout its scanning field in the x-y plane. In addition, scanning inthe z direction is largely decoupled from scanning in the x-y plane.

In general, a flexure stage refers to a planar platform consisting of aplate formed of material capable of being flexed (generally a metal suchas aluminum or stainless steel). One or more flexible members aremachined into the platform which serve as spring elements. The springelements connect a stationary portion of the platform to a movingportion of the platform. A piezoactuator is coupled to the platformwhich serves as a drive mechanism to push the moving portion of theplatform relative to the stationary portion of the platform. U.S. Pat.No. 4,506,154 describes the design and manufacturing of examples offlexure stages which may be used in the present invention and isincorporated herein by reference.

In a uniaxial flexure stage, the one or more flexible members allowmovement along a single translational degree of freedom and are veryrigid in the remaining five degrees of freedom, thereby minimizingmovement along the two other translational degrees of freedom and in thethree rotational degrees of freedom.

The incorporation of one or more pivoted lever arms into the platformprovides a mechanical amplification factor for extension and contractionof the piezoactuator. When one internal spring of the flexure plate ispushed and displaced a certain distance by the piezoactuator, the one ormore pivot lever arms push against each other and an amplifieddisplacement can be measured at another location on the plate. Themechanical amplification factor depends on the structure of the machinedin spring elements and pivot arms as is well known in the art.

A flexure stage can have a variety of objects mounted on it which aremoved by the actuation of the stage. In the present invention, a varietyof components of the SPMs or SPM heads can be mounted on the flexurestage, including for example, the probe or sample; components of acantilever deflection sensor; components of a position sensor forflexure stage motion; and another or multiple flexure stages.

FIG. 5 illustrates an embodiment of a flexure stage which providesmotion in a single translational direction. It should be noted that awide variety of designs may be used for a flexure stage which are withinthe level of ordinary skill and are intended to fall within the scope ofthe present invention.

As illustrated in FIG. 5, the flexure stage includes an outer frame 60and an inner portion 62 which can be moved relative to the outer frame60. Included on the inner frame are mounting points 67 for mounting asecond identical flexure stage which is orthogonal to the first stage.The outer frame 60 and inner portion 62 are coupled to each other bymachined-in spring elements 64. Also incorporated into the inner portion62 are multiple pivoted lever arms 66 with pivot points 63. When anactuator 68 is positioned within the slot 70 and coupled to the multiplepivoted lever arms 66, any displacement of the actuator 68 is amplifiedby the multiple pivoted lever arms 66, thereby causing increasedmovement of the inner portion 62 relative to the outer frame 60 which ismeant to be fixed. The gain factor g for this flexure stage, obtainedusing the lever amplification principle, is given by g=b/a·d/c, where a,b, c, and d are the distances indicated in FIG. 5.

A stacked piezoelectric actuator is often used as the actuator fordriving the flexure stage. For a given form factor (shape, relativedimensions), a stacked piezoelectric structure consisting of a series ofpiezoelectric plates glued or cemented together produces a greatertransmittal motion, or extension (throw), than a single plate sincepiezoelectric displacement varies inversely with thickness of apiezoelectric plate. A stacked piezoelectric actuator also produces alarger actuation force allowing it to push on a relatively stiffmechanism.

In general, stacked piezoactuators alone cannot support a large masssince a large shear force can shear the glued piezoelectric platesapart. However, when the flexure stage is machined out of stainlesssteel or aluminum, the flexure stage is able to support greater weightthan the piezoactuator alone. As a result, the combination of apiezoactuator with a flexure stage provides well-controlled motion andthe capability to carry loads up to 50 g or more. Instead ofpiezoactuators, other types of actuators including motors, voice coils,lead screws, and others, can be used.

FIG. 6 illustrates an embodiment of a single-plate biaxial flexure stagewhich provides motion in two translational directions. The single-platebiaxial flexure stage 61 illustrated in FIG. 6 includes an outer frame78 and two inner portions 65 and 69 which are interconnected viamachined-in spring elements 71 and 74 which provide restoring forces.Piezoactuator 72 pushes inner portion 65 relative to fixed outer frame78 to move inner portion in the x direction. Likewise, piezoactuator 76pushes inner portion 69 relative to inner portion 65 in the y direction.The net effect of this motion is that inner portion 69 is translated inboth the x and y directions.

Scanning in the x-y plane is preferably accomplished in the SPMs and SPMheads of the present invention by using either a single-plate biaxialflexure stage, such as the one illustrated in FIG. 6, or by using astacked flexure stage formed from two orthogonally mounted flexurestages, such as the one illustrated in FIG. 5, which each provide motionin a single translation direction.

FIG. 7 illustrates a stacked x-y flexure stage 90. As illustrated, thex-y flexure stage 90 includes a flexure stage 92 for providing motionalong the x axis and a flexure stage 94 for providing motion along the yaxis. The outer frame 96 of the y flexure stage 94 is fixed in space andthe inner portion 98 of the stage can be moved along the y axis.Meanwhile, the inner portion 98 of the y flexure stage 94 is attached tothe inner portion 100 of the x flexure stage 92. The outer frame 102 ofthe x flexure stage 92 can be moved along the x axis relative to theinner portion 100. By coupling the movement of the inner portion 98 ofthe y flexure stage 94 to the inner portion 100 of the x flexure stage92, the outer frame 102 of the x flexure stage 92 can be moved alongboth the x and y axes relative to the outer frame 96 of the y flexureframe.

A single actuator, preferably a stacked piezoactuator, is used with eachof the x and y flexure plates to provide a scanning motion along the xand y axes. The design of the flexure stages provides a mechanicalamplification of about 10:1; i.e., for a certain extension/contractionof a piezoelectric actuator, the outer frame 102 is moved a distance 10times greater.

One of the advantages of x-y flexure stages is that they produce ahighly planar scan in the x-y plane without appreciable bowing. As aresult, it is possible to use a scan stage oriented for motion along thez axis which is off center relative to the center of movement of the x-yscanning stage without having x-y scan motion introduces errant motionin the z direction. Typical maximum x-y scan sizes using a stacked x-yflexure stage of this invention are from 100 μm to 200 μm, with z rangesof 10 μm to 20 μm and bowing motion on the order of only a few tens ofmillimeters (approximately 50 nm at full scale, with the z stagedisplaced from the center of x-y translation by about 3″). This is atremendous improvement over existing SPM scanners, providing greatflexibility to choose a scan size for SPM imaging.

The use of a stacked x-y flexure stage is preferred over a single platebiaxial flexure stage in view of the higher linearity of the scan thatis provided. Stacked x-y flexure stages have been found to producenearly orthogonal motion in the x-y plane (about 2° or less which isbetter than the performance of single plate biaxial flexure stages).Stacked x-y flexure stage also minimize cross-coupling between the x, y,and z axes by mechanically decoupling motion in these directions.

Tripod scanners and piezoelectric tube scanners have traditionally beenused in SPMs. As illustrated in FIG. 8, the three legs 81, 83, 85 of atripod scanner 87 are joined at the apex 89. As a result, scanningmotion provided by a tripod scanner in the x, y, and z directions ishighly coupled. If single-element piezoelectrics are used for each leg(U.S. Pat. No. 4,908,519, tripod scanners have a small throw, or maximumrange of extent. The throw provided by a tripod scanner can be increasedby using stacked piezoelectric elements. However, x, y, and z couplingincreases with increased throw. Tripod scanners also have thedisadvantage of being too weak to carry large loads, since they havelittle shear strength.

The scanning motion of a piezoelectric tube scanner is illustrated inFIGS. 9A-9B. As illustrated, tube scanners also exhibit x, y, and zcoupling and a non-planar x-y scanning motion. G. Binnig and D. P. E.Smith, Rev. Instrum., 57, pp. 1688 (1986). The x, y, and z couplingobserved in a tube scanner is due, in part, to the fact that the scannerscans in an arc which is determined by the tube's length. The tubescanner's bowing motion shown in FIG. 9A produces cross-coupling betweenx-z and y-z motion that shows up as curvature in an SPM image. The widerthe scan in x and y, the greater the amount of bowing, which increasesapproximately quadratically with distance from the center of the scan.

The x, y, and z coupling observed in tube scanner is also due apush/pull effect illustrated in FIG. 9B in which opposite sides of thetube contract or extend during motion in the x-y directions, thusproducing out-of-plane tilting. The amount of z displacement observed isalso a function of the displacement of the tube scanner from the centerof (x,y) motion.

The z scanner must generally compensate for changes in the probe'sposition along the z axis due to nonplanar scanning motion by the probealong the x and y axes. As a result, a portion of the scan range alongthe z axis must be reserved to perform this correction which ultimatelylimits the maximum z range available to scan a sample's topography.Consequently, the entire z range of the tube scanner is not available toimage sample topography. For example, if a probe were mounted 3 inchesoff the center of x-y motion on a tube scanner, it would not be possibleto scan 100 μm in the x or y direction because the z range of thescanner would not be sufficiently great to compensate for the bowingintroduced by the tube scanner.

The length of tube scanners has the further disadvantage of limiting howclosely optical components can be brought to the probe and sample. Useof an x-y flexure stage provides a lower height profile than a tubescanner and reduces constraints on the positioning of objective andcondenser lenses relative to the sample and probe.

X-Y Flexure Stage with Off Center Z Scanning Stage

Another important aspect of the present invention is the use of zscanning stages which are positioned off center relative to a x-yflexure stage.

Z scanning stages in an SPM are typically located at the center of x-ymotion of an x-y scanning stage in order to decouple any non-planarityin the x-y scan from the z scan. A scanner with a z scanning stagepositioned at the center of x-y motion has the additional advantage ofbeing easy to build.

As illustrated in FIG. 10, one problem associated with positioning a zscanning stage 104 at the center of motion of an x-y scanning stage 107is that it is necessary to make a hole 110, in the x-y scanning stage107 in order to view the sample 114 and the probe 116.

Since the working distance of a standard objective lens and also ofcondenser lenses used in inverted optical microscopes is on the order of20 mm, the thickness 112 of a x-y scanning stage 107 limits how closelyan objective lens or illumination source can be brought relative to asample 114 or a probe 116.

The problem of not being able to bring objective lenses into closeproximity with the sample or probe can be overcome by using a longerworking distance lens. However, such non-standard lenses are moreexpensive and produce a lower quality optical image. The hole 110 in thex-y scanning stage 107 can also be made large enough to accept astandard long working distance objective. However, since the diameter ofthe lens is typically on the order of 1¼″, increasing the width of thehole 110 in the x-y scanning stage 107 in order to accommodate anobjective or condenser lens causes the lateral footprint of the x-yscanning stage 107 to be increased. Increasing the lateral footprint ofthe x-y scanning stage, in turn, requires that the piezoactuators andthe feet of the stage be moved further apart. In an SPM, a small lateralfootprint is more desirable because it decreases the mechanical loop ofthe system, thus providing greater mechanical stability. By enlargingthe lateral footprint of the stage in order to accommodate an objectivelens, the performance of the SPM may be compromised.

The hole in the center of the x-y scanning stage may also serve tofacilitate access to the sample and probe for manipulation by a varietyof tools. However, access to the sample and probe through the holerequires that the tools be operated at high angles relative to the planeof the sample and with a blocked or impaired optical view. As a result,the configuration illustrate d in FIG. 10 where the x-y scanning stageincludes an access hole is not highly compatible with micromanipulationsof samples which require a simultaneous optical view.

In the present invention, as illustrated in FIGS. 1-4, the use of ahighly planar x-y flexure stage, in contrast to piezoelectric tubescanners and tripod scanners, enables a separate z scanning stage to beused which is positioned off the center coordinates of x-y motion (0,0)and more preferably outside the lateral footprint of the x-y flexurestage. Since the z scanning stage may be mounted off to the side of thex-y flexure stage, the probe can be mounted in a position relative tothe x-y stage where top down and bottom up optical views of the probeand sample are not obstructed by the x-y stage. In addition, theconfiguration of the z scanning stage off center enhances access to thesample and probe.

Z Flexure Stages

The SPMs and SPM heads of the present invention may also include aflexure stage which provides scanning motion along the z axis.

An embodiment of a z flexure stage is illustrated in FIG. 11. Asillustrated, the stage includes a fixed portion 91 and a moving portion93 which is attached to the fixed portion 91 by spring elements 95. Anactuator 97, illustrated as a stacked piezoactuator, pushes movingportion 93 relative to fixed portion 91. A bracket 100 for mounting aprobe (not shown) on the z flexure stage and a bracket 99 for mountingthe z flexure stage on the x-y scanning stage may be attached to the zflexure stage. A z flexure is used to drive a high load at relativelyhigh speeds.

In another embodiment, multiple z flexure stages are attached to the x-ystage in order to incorporate multiple probes onto the SPM or SPM headfor simultaneous probing and/or processing. For example, multiple probesare useful for performing nanolithography since multiple areas can beprocessed in parallel. In a preferred variation of this embodiment, themultiple z flexure stages are positioned outside the lateral footprintof the x-y scanning stage as described below.

Off-Center Z Flexure Stage

In a preferred embodiment of the invention, the z flexure is positionedoff the center of the x-y translation of the x-y scanning stage. Severalconfigurations of a x-y scanning stage with a z flexure positionedoff-center can be envisioned and are intended to fall within the scopeof this invention. In a particularly preferred embodiment, the z flexureis positioned outside the lateral footprint of the x-y stage.

FIG. 12 illustrates a lateral view of an SPM head where the z flexurestage is positioned outside the lateral footprint of the x-y stage. Asillustrated, SPM head 12 includes an z flexure stage 116 which isattached to an x-y scanning stage 118 having legs 119. A bracket 121carrying a probe 126 and a detection system 123 is mounted on the zflexure stage.

The x-y scanning stage 118 is illustrated in the figure as a stacked x-ystage including x flexure stage 120 and y flexure stage 122. In additionto a stacked x-y flexure stage or a single plate biaxial x-y flexurestage, any another type of x-y scanning stage which provides a highlyplanar scan along the x-y plane can be used.

Stacked x-y flexure stages provide an advantage over single platebiaxial x-y flexure stages of being more readily designed with a smallerlateral footprint. This smaller footprint provides the stacked x-y stagewith greater mechanical stability and makes the stage less susceptibleto thermal drift. Stacked x-y flexure stages also exhibit greaterdecoupling in the x, y, and z scan directions than biaxial x-y flexurestages and thus provide more highly planar and orthogonal scans. Inaddition, two identical stacked uniaxial flexure plates are lessexpensive to manufacture than a biaxial flexure stage.

As shown in FIG. 12, the z flexure stage is positioned outside of thelateral footprint 124 of the x-y scanning stage 118. A probe 126 isattached to the z flexure stage 116 which extends over a sample 128. Theprobe is also preferably outside of the lateral footprint of the x-yscanning stage 118 and is preferably also outside the lateral footprintof the z flexure stage.

As illustrated in FIG. 12, by attaching the z flexure stage 116 outsideof the lateral footprint 124 of the x-y scanning stage 118, an objectivelens 130 may be readily positioned at a close working distance relativeto the probe 126 and the sample 128. As also illustrated in thisembodiment, the objective lens 130 may be positioned above or below 130′the probe 126 and sample 128 to provide unobstructed top down and/orbottom up optical views of the probe 126 and sample 128. A condenserlens could alternatively be positioned where objective 130 is located.

In addition to providing unobstructed top down and/or bottom up opticalviews, designing the stage so that the z flexure stage is outside of thelateral footprint 124 of the x-y scanning stage 118 enables enhancedaccess to sample for manipulating the sample under simultaneous opticalviewing.

For a given throw in x, y, and z, a scanning stage of the presentinvention which includes a stacked x-y flexure stage coupled to a zflexure stage has a lower height profile than a tube scanner. For agiven load, given voltage, or given profile, this scanning stageprovides a larger throw relative to tube scanners or stackedpiezoelectric actuators alone.

The typical load that may be supported by this scanning stage, includingthe mass of the cantilever, the optical detector, and the laseralignment system, is about 50 g or more.

The bracket 121 used to attach the probe 126 to the z flexure stage mayhave a variety of configurations such as those illustrated in FIGS. 2and 3. The bracket 121 may also be designed to include a detectionsystem for the SPM or SPM head.

Optical Viewing

Commercially available optical microscopes generally collect imagesusing either (or both) epi or transmitted illumination. Epi illuminationmeans that the image is collected from light that is reflected,scattered, or emitted (in the case of fluorescence) from the sample.When epi illumination is used, the illumination source and the objectivelens are on the same side of the sample. The objective may be used forboth illuminating the sample and collecting the image. Upright opticalmicroscopes generally provide epi illumination and can also provideKohler illumination.

Transmitted illumination means that the light source and the objectiveare on opposite sides of the sample, so that light collected for theimage has been transmitted through the sample. This is also known asKohler illumination. Inverted optical microscopes generally providetransmitted or Kohler illumination, but can provide epi illumination aswell, by using the inverted objective lens to provide both illuminationand image collection.

As described above, the SPMs and SPM heads of the present invention aredesigned to enable unobstructed viewing from both above and below theprobe and sample. When x, y and z flexure stages are employed, thescanning stage also provides a sufficiently short working distance toenable standard long working distance lenses to be used. As a result, anobjective lens and an illumination source may be positioned relative toprobe and sample to provide either epi or transmitted illumination withsimultaneous probe scanning.

In a preferred embodiment, both a condenser lens and objective are used,above and below the plane of the sample, respectively, and centeredroughly around the probe position, for Kohler illumination and forcollection of transmitted light using an inverted optical microscope. Inthis inverted configuration, the condenser lens supplies high intensitylight, which is transmitted through a translucent or transparent sampleand collected by an objective underneath. In both the upright andinverted configurations, the objective lens both illuminates andreceives light scattered back from the sample. Upright opticalmicroscopes using epi illumination do not require samples to betransparent.

The design of the SPMs and SPM heads of the present invention enablesimultaneous probe-scanned SPM with an unobstructed optical viewobtained without the assistance of a mirror. Also enabled issimultaneous probe-scanned SPM and epi illumination using standardcommercially available upright optical microscope. Also enabled issimultaneous probe-scanned SPM and transmitted illumination usingstandard commercially available inverted optical microscope. Alsoenabled by the design of the SPMs and SPM heads of the present inventionis simultaneous probe-scanned SPM and all the optical modes provided bystandard commercially available inverted optical microscopes.

Detection System

The SPMs and SPM heads of the present invention may incorporate a widevariety of detection systems used in combination with a probe forprobing a surface. The particular detection system incorporated into anSPM or SPM head depends on the type of probing to be performed. Asdiscussed above, the SPMs and SPM heads of the present invention may beused to perform any type of scan probe microscopy including, but notlimited to contact atomic force microscopy (AFM), non-contact AFM,lateral force microscopy (LFM), scanning tunneling microscopy (STM),magnetic force microscopy (MFM), scanning capacitance microscopy (SCM),force modulation microscopy (FMM), electrostatic force microscopy (EFM),and other modes of operating a scanning probe microscope. The detectionsystem incorporated into the SPM and SPM head is preferably selected tobe particularly well suited for the type of microscopy to be performed.

In a preferred embodiment of the present invention, the detection systememployed is a dual mirror optical deflection detection system. It shouldbe noted, however, that a variety of other detection mechanisms may beused, including, but not limited to piezoresistive capacitive and thelike. As illustrated in FIGS. 13A-13B, the detection system includes twosteerable mirrors, one mirror 130 to steer the laser beam 132 from laser133 onto the cantilever 134, and the second mirror 136 to steer thereflected beam 138 onto the detector 140. The detection system ismounted on a z flexure stage 137 by bracket 135.

The two mirrors 130,136 may each be steered by mechanisms which are wellknown in the art.

As illustrated in FIGS. 13A-13B, the laser 133 in this detection systemis horizontal, i.e., approximately parallel with the x-y plane. Thisorientation minimizes the laser's dimensions along the z axis. Since thelaser 133 is long (about 20 mm), mounting the laser vertically directlyover the probe, as illustrated in FIG. 14A, would block the use of astandard long working distance objective 139. If the laser 133 wereoriented vertically but offset from the probe, as shown in FIG. 14B, atleast two mirrors 141, 142, one of them a beamsplitter, would benecessary to steer the laser beam 132 onto the back of the cantileverprobe 134 to produce a top down view. The laser can also be tiltedrelative to the z axis so that a mirror would not be necessary to steerthe laser beam onto the cantilever. However, this orientation increasesthe height profile relative to the perfectly horizontal.

Laser light reflected from the cantilever probe 134 is directedapproximately horizontally towards a position-sensitive photodetector140 from the second mirror 136. The position-sensitive photodetector 140is preferably mounted vertically relative to the x-y stage, asillustrated in FIG. 13B in order to detect vertical displacement of thelaser beam on the photodetector 140.

In one embodiment, a quad-cell position-sensitive photodetector (PSPD)is used as the photodetector which allows deflection detection for allthe SPM modes, both contact and non-contact, including lateral forcemicroscopy (LFM). With provision for biasing or grounding the tip, STMand EFM is also possible. A bi-cell photodetector could also be used todetect cantilever displacement but it would not allow LFM operation aswell.

With the design for the dual mirror optical deflection detection system,as illustrated in FIGS. 13A-13B, the diameter of the laser 133 and thephotodetector 140 are the limiting factors with regard to the heightprofile of the detection system, as illustrated in FIG. 15. In general,the diameters of the laser 133 and the photodetector 140 are about 8 mm.

In order to reduce the height profile of the detection system, the laser133 can be replaced with an optical fiber and the laser light reflectedfrom the cantilever probe can be collected using a second fiber opticand a lens. This design could further reduce the height profile of thedetection system down to a few millimeters. In this alternativeconfiguration, mirrors 130 and 136 would still be needed to steer thelaser beam onto the back of the cantilever and from the cantilever ontothe photodetector.

In yet another embodiment, the laser and photodetector are moved in thex-y plane away from the probe in order to reduce the height profile ofthe detection system directly adjacent the probe thereby reducing theworking distance for an objective or condenser lens.

An unique aspect of the dual mirror optical deflection detection system,as illustrated in FIGS. 13A-13B, is that the area above the cantileverprobe 134 is unobstructed. This is made possible, in part, by the use ofthe two mirrors 130, 136 and laser 133 oriented horizontally relative tothe x-y stage 135. As a result, the space substantially above thecantilever probe 134 is free for both illumination (for instance, byconfocal microscopes, lasers, etc.) and for direct optical inspection.This configuration also allows the SPM to be combined with otherinspection tools such as optical micrometers, optical scatteringdevices, and any inspection apparatus where it is necessary to view oraccess the sample from directly above.

Closed Loop Scanning System

FIG. 16 illustrates the incorporation of a closed loop scanning systeminto the SPMs and SPM heads of the present invention. As illustrated,two light emitting diodes 150, 152 are mounted on a fixed portion of thex-y flexure stage 154 facing two photodetectors 155, 156 which aremounted on the z flexure stage 158. One of the photodetectors 155 is aquad-cell position sensitive photodetector (PSPD) and is used to sensex-y positioning while the other photodetector 156 is a bl-cell PSPD andis used to sense the z positioning of the probe. Examples of electronicsand design consideration that may be used to implement the closed loopscanning system are described in U.S. Pat. Nos. 5,376,790 and 5,210,410which are incorporated herein by reference. Using this closed loopscanning system, scanning in x and y can be corrected in real-time forscanner nonlinearities such as creep and hysteresis. Z positiondetection also enables an image to be generated using the z detectorsignal.

Course Stage Adjustment

An SPM or SPM head of the present invention may be kinematically mountedon a coarse x-y mechanical stage which enables alignment of the probe171 within the field of view of an objective lens 175 of an upright orinverted optical microscope 177. As illustrated in FIG. 17, an SPM head,which includes an x-y scanning stage 179, a bracket 181, a z scanningstage 183, and a probe 171, is supported on three legs 170, 172, 174.The curved surfaces of the legs contact a cone 176, a slot 178, and aflat 180 located on an optical microscope stage plate 177 to form akinematic mount which allows approximately orthogonal x-y translation. Afurther description of a kinematic mount such as the one illustrated inFIG. 17 is described in U.S. Pat. Nos. 5,157,251 and 5,376,790, whichare incorporated herein by reference.

Manual translation in the x and y directions is produced by turning twothumbscrews 184, 186 located on the optical microscope plate 177, whichpush or pull guide pieces 182, 173 along dovetail tracks containing thecone and the slot. The coarse x-y stage can also be motorized.

Using the kinematic mount described above, existing upright and invertedoptical microscopes may be readily retrofitted to be combined with anSPM or SPM head of the present invention by replacing the existingoptical microscope stage plate with a stage plate modified to includekinematic mounting points and a mechanism for adjusting their position.

As illustrated in FIG. 18A, the three supporting legs used in thekinematic mount may be formed of the ball-tips of three screws 186, 187,188 which form a coarse z mechanical stage used to raise and lower theSPM head 190 in the z direction in order to perform a tip-to-sampleapproach. The design of the coarse stage adjustment allows for both amanual and automatic approach. The manual approach may be accomplishedusing all three screws 186, 187, 188 to lower the SPM head 190 (x-yflexure stage 191, probe 192, z flexure stage 193, bracket 195) untilthe probe 192 is in close proximity to but not touching the sample 194(as determined by eye), and then using a single screw to further tiltthe head until the probe is engaged. An automatic approach can also beperformed which uses a motor 196 to turn on one of the screws to performthe same tilting action as in the manual approach. Alternatively, allthree approach screws can be motorized using one or more z motors.

The motor 196 used for the z approach is preferably a piezoelectricallydriven screw, such as PICOMOTOR™ from Nufocus, Inc. although other typeof motors can be used. This type of inertial driven motor is small andcompact, and provides a low profile, reduced weight, and high resolution(about 30 nm/step). The motor has no appreciable backlash in comparisonto stepper motors which produce heat and vibrations leading to backlash.

As illustrated in FIGS. 17, 18A-18B, the SPM or SPM head may alsoinclude a mechanism, referred to herein as a locking jack 189, whichenables the user to lift and tilt the SPM head relative to the samplestage and lock the head into a raised position for quick access to thesample and probe.

As illustrated, the locking jack mechanism includes an arm 200 and aspring 202 which biases two or more legs (illustrated as screws 187,188) against a surface on which the SPM head is placed, illustrated inFIGS. 18A-B as optical microscope stage 204. As illustrated in FIG. 18B,when one end of the SPM head is raised, two or more of the legs oppositethe raised end act as pivot points. The arm 200 includes a lockingmechanism 206 which holds the SPM head in the raised position.

The steps to lift the SPM head in order to replace the probe 192include: (1) moving the objective or condenser lens from the space aboveSPM head; (2) tilting the SPM head upward until the locking mechanism ofthe locking jack engages; (3) removing the probe and replacing it; (4)disengaging the locking mechanism; and (5) lowering the SPM head untilthe legs contact the kinematic mounting points.

Because the legs of the SPM head are lowered onto kinematic mountingpoints on the optical microscope stage whose positions are not alteredby the process of raising and lowering the SPM head, the probe may bereadily replaced and/or the sample manipulated without having to adjustthe position of the probe relative to the sample.

Sample Stage

FIGS. 19A-19C illustrate embodiments of sample stages and sample stageholder designed for use in biological applications of scanning probemicroscopy.

FIG. 19A illustrates a sample holder 206 which includes slots 208 and210 sized to accommodate a coverslip or slide in addition to adepression 212 which is sized to accept a Petri dish. Two spring clips214 and 216 secure a slide in slot 210. The sample holder couldalternatively be designed to accommodate only a coverslip, a slide, or aPetri dish.

FIG. 19B illustrates a sample holder 218 which includes multiple slots220 sized to accommodate a series of coverslips or slides. The sampleholder 218 may also include spring clips 222 for holding slides inplace.

FIG. 19C illustrates a sample holder 224 which includes multipledepressions 226 sized to accommodate a series of Petri dishes. In thisembodiment, the multiple depressions are preferably positioned on acarousel-type wheel 228 which can move the different depressions intoposition for scanning or observing. Such a carousel-type wheel may alsobe used to move a series of slides or coverslips into position on sampleholder 218 in FIG. 19B.

As illustrated in FIGS. 20A and 20B, sample holder 206 may be positionedwithin a ring member 205 which is slidable on optical microscope stage207 or another sample stage. Ring member 205 fits around the sampleholder 206, which may include a depression 219 which accepts a samplemounted on a coverslip, slide, or Petri dish. Ring member 205 is sizedsuch that it is able to leave a gap along all the sides of the sampleholder. By moving ring member 205, it is possible to move sample holder206 in the x-y plane on optical microscope stage 207. Because the ringhas larger dimensions than the sample holder, the translation mechanismhas a high degree of play in it, so that the sample holder can bedisengaged from ring member 205 for greater mechanical stability duringSPM imaging.

Ring member 205 may be moved using a conventional x-y translation stage209, for instance a dual rack and pinion stage such as in a Zeissoptical microscope, although any conventional translational stage can beused. In the embodiment illustrated in FIG. 20B, x-y translation stage209 includes an x translation arm 211 mounted on a y translation arm213. Ring member 205 is attached to the x translation arm via screw 215.When the x-y translation stage 209 is moved, ring member 205 pushessample holder 206 in the x or y direction (or both) so that it slides indirection of motion 217.

The sample holder is secured to the base of the optical microscope usingmagnets 221 as shown in FIGS. 19A and 20A to provide stability duringSPM imaging. Optical microscope stage 207 is magnetic stainless steel,and four magnets 221 are attached to the underside of the sample holder.Three balls 223 on the underside of the sample holder provide threepoints of contact (feet) to define a constant plane and also to reducefriction as the sample holder is translated in the x-y plane. Themagnets are therefore not in physical contact with the base of theoptical microscope. With a little sideways force, the magnetic force canbe overcome and the sample holder can slide along the base of theoptical microscope. Vacuum suction could also be used in place ofmagnets. Typically, Petri dishes are held onto the sample holder bygravity; the additional magnetic forces provide enhanced stability.Coverslips may be secured to the sample holder using vacuum grease.

Liquid Cell/Cantilever Chip Holder

An important application of the SPMs and SPM heads of the presentinvention is in the performance of scanning probe microscopy in with asample immersed in liquid, which is especially useful for biologicalsamples. Illustrated in FIGS. 21A-21C is a combined liquidcell/cantilever chip holder for use in an SPM or SPM head.

The liquid cell 210 illustrated is of a captured-drop type in which adrop of liquid 229 surrounds the probe 233 and sample 234 and is held bysurface tension between a viewport 235 on the underside of the liquidcell 227.

As illustrated in FIG. 21A, the liquid cell 227 includes walls 218 whichare preferably sized to fit beneath a condenser lens or objective of anoptical microscope. The walls 218 illustrated in the figure form ahollow square pyramid-shape. However, alternative shapes, for example around (cone-shaped) liquid cell can be used. The walls serve to confineliquid to the outer surface of glass viewport 235.

At the bottom of the walls 218 include a viewport 235, generally glass,through which the cantilever probe 233 and sample 234 are viewed. Theviewport 235 has very low replacement cost and can be removed forstandard ambient imaging conditions.

The liquid cell 227 has a tapered design with a very small overhangabove the cantilever probe 233 and sample 234 which gives the liquidcell 227 a small footprint for better access to the probe-sample area.It is desirable to provide convenient sample access for variousinstruments 237 such as micromanipulators, patch clamp pipettes, andother tools used for micromanipulation of cells. Without the tapereddesign, access to the sample from above would be blocked, andinstruments used for micromanipulation of samples would need to beinserted sideways, which is inconvenient.

As illustrated in FIG. 21A, the tapered design of the fluid cellprovides a clear path for the laser beam 241 of the deflection detectionsystem 244 (laser 245, mirrors 247, 250, and photodetector 225) whichpasses through a viewport 235 and liquid 229 to the cantilever probe233.

As illustrated in FIG. 21B, indentations 252 can be made along thelength of the walls 218 to allow even easier access to the sample 234using a long narrow tool.

As illustrated in FIG. 21C the liquid cell can be designed to be openedup laterally to allow decreased lens working distance. This embodimentis particularly useful if tools are not needed to manipulate the sample.In this embodiment, liquid cell walls 254 are slanted outwards making asmaller angle with the plane of the sample, and the components of thedeflection detection system 244 (laser 245, mirrors 247, 250, andphotodetector 225) are moved further back from the liquid cell walls.Opening up the liquid cell laterally in this manner (making it wider sothat a lens can be brought closer to the probe) is one way to reduce theheight profile and thus the working distance required. The heightprofile desired depends on the depth to which the liquid cell isintended to be submerged in liquid. For some applications, the liquidcell may be submerged in liquid to a depth of several millimeters, forinstance in a Petri dish. The deeper the cell is to be submerged, themore height is needed for the walls of the liquid cell, to preventliquid from spilling onto the opposite surface of the glass viewport,where any droplets can interfere with optical viewing and laseralignment.

The liquid cell could also include a shroud to prevent liquidevaporation. The shroud could be a flat ring or umbrella such as arubber containment ring which surrounds the liquid cell to cover theliquid.

Kinematic Mount of Liquid Cell/Cantilever Chip Holder

The combined liquid cell/cantilever chip holder is preferably mountedkinematically to an SPM head as illustrated in FIG. 22. The kinematicmount consists of three balls 230, 231, 232 on the top surface 256 ofthe cell/holder assembly 236. These balls contact a cone 238, a slot240, and a flat 242 on a lower surface 243 of the SPM head 258. A magnet246 on the cell/holder assembly 236 secures the assembly against aferromagnetic material 248 in the SPM head 256. Alternatively, magnetsmay be attached to the assembly and to the SPM head.

The magnetic force provided by the magnet 246 and ferromagnetic material248 is sufficient to self-seat the assembly 236 in the kinematic mountand is stable enough during SPM imaging to provide nanometer-scaleresolution. By using magnetic force to seat and retain the assembly, theentire assembly can be removed by hand, for example, to replace acantilever. No special tools are required. Because of the quick-snapself-seating mechanism of the assembly, cantilever replacement is easyand quick, taking only a few seconds to perform. This feature isadvantageous for use in a variety of applications including insemiconductor process control equipment and applications. Thisattachment mechanism can also be adapted for use in an automatic tipchanger.

Both mounted and unmounted cantilevers can be used in the assembly. Thekinematic mount of the cantilever holder gives 1 to 2 μm alignmentrepeatability when the same cantilever is replaced. When unmountedcantilevers are exchanged, the new cantilevers are aligned to within 10to 100 μm after insertion.

FIG. 23A illustrates a cantilever 260 directly mounted to a holder 262.FIG. 23B illustrates a cantilever 264 kinematically mounted to a holder266. As illustrated, the kinematic mount is formed of three balls 267,268, 269 and complementary slots 270, 271, 272. Use of a kinematic mountfor mounting the cantilever to the holder is preferred since it wouldincrease alignment accuracy to within 10 to 20 μm. A spring clip 249 isillustrated for holding the cantilever in place.

The combined liquid cell/cantilever chip holder could also be used withspecial engineered cantilevers which allow microinjection of substances.For example, a cantilever holder could be adapted to accept pulledpipette cantilevers with a sharp enough tip so that SPM imaging is stillpossible. The invention could also be combined with existing hollow tipcantilevers to allow microinjection of substances.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than limitingsense, as it is contemplated that modifications will readily occur tothose skilled in the art, which modifications will be within the spiritof the invention and the scope of the appended claims.

What is claimed is:
 1. An optical microscope stage comprising: a samplestage having a horizontal surface on which a sample holder may bepositioned; a coarse x-y control stage for supporting a head of ascanning probe microscope (SPM) above the sample stage and moving theSPM head relative to the sample stage; and a member positioned adjacentthe horizontal surface of the sample stage, the member comprising aninternal perimeter that defines an interior space which allows a sampleholder to be positioned on the horizontal surface of the sample stagewithin the internal perimeter, the member being laterally movablerelative to the horizontal surface independent of the sample holder suchthat the member repositions the sample holder relative to the horizontalsurface by laterally pushing the sample holder without lifting thesample holder, the interior space defined by the inner perimeter of themember being sufficiently large that the sample holder may be within theinterior space without contacting the internal perimeter of the member.2. An optical microscope stage according to claim 1, wherein the coarsex-y control stage includes a kinematic mount for a SPM head.
 3. Anoptical microscope stage according to claim 2, wherein the kinematicmount includes a cone, a slot, and a flat.
 4. An optical microscopestage according to claim 1, wherein the optical microscope stage furtherincludes a locking jack for raising and lowering an SPM head relative tothe course x-y control stage.
 5. An optical microscope stage accordingto claim 1, further including a sample holder.
 6. An optical microscopestage according to claim 5, wherein the sample holder is magneticallyattached to the sample stage.
 7. An optical microscope stage for use asa sample stage of a scanning probe microscope (SPM), the opticalmicroscope stage comprising: a horizontal surface on which a sampleholder may be positioned; a member positioned adjacent the horizontalsurface of the sample stage, the member comprising an internal perimeterthat defines an interior space which allows a sample holder to bepositioned on the horizontal surface of the sample stage within theinternal perimeter, the member being laterally movable relative to thehorizontal surface independent of the sample holder such that the memberrepositions the sample holder relative to the horizontal surface bylaterally pushing the sample holder without lifting the sample holder,the interior space defined by the inner perimeter of the member beingsufficiently large that the sample holder may be within the interiorspace without contacting tie internal perimeter of the member.
 8. Anoptical microscope stage according to claim 7, further including asample holder.
 9. An optical microscope stage according to claim 8,wherein the sample holder is magnetically attachable to the opticalmicroscope stage.